Add "common issues" doc to cover known workarounds

[sirosen]

I'm happy to write a first draft of this if the maintainers would like it. But I don't want to put in the effort if it's not wanted.

I've run into two issues which really puzzled me in terms of what to do until I poked around in issues here. I'm sure there are others.

hybrid_property can't use the special magic of property in mypy, but #98 has a workaround seems to work. And #94 covers ways of getting UUID(as_uuid=True) to work.

It would be helpful (since these are not going to be fixed soon) if this library made these workarounds part of its docs. It could be done at the end of the readme or in a separate markdown doc linked in the repo.

[absassi]

#114 also has a workaround for Enum.